This invention relates generally to icemakers, and more particularly to control systems for icemakers in refrigerators.
Known icemakers typically include a number of electromechanical elements that manipulate a mold to shape ice as it freezes. For example, a heater is used to heat the mold to allow release of ice cubes, and a motor rotationally drives a rake to remove ice cubes from the mold and into an ice bucket. See, for example, U.S. Pat. Nos. 4,429,550 and 4,838,026, both of which are assigned to the present assignee. Cam driven switches and a thermostat are typically used to determine when to harvest ice from the mold, and also for opening and closing a water valve to fill the mold with water once a harvest cycle is complete.
Such icemakers, however, are disadvantageous in several aspects. For example, cam driven water valve controls are not as accurate as desired, so that each control must be calibrated for each icemaker that is produced. Also, fluctuating water pressure can render cam driven water valve controls ineffective. Furthermore, known icemakers are vulnerable to jamming during harvest operations.
In an exemplary embodiment of the invention, an electronic controller is provided for an automatic icemaker including a mold, a heater coupled to the mold, a rake for ejecting ice from the mold, and a feeler arm in communication with an ice storage bin. The controller includes a thermistor in fluid communication with the mold to determine a temperature of ice, water, or air in the mold, a first transducer coupled to the rake for sensing a position of the rake, a second transducer coupled to the feeler arm for determining a position of the feeler arm, and a processor coupled to the first transducer, the second transducer, and the thermistor.
In one aspect of the invention, the processor is programmed to execute a freeze state for freezing water in the mold in which a temperature input value is calculated at successive time intervals. The calculated values are cumulatively summed at each successive time cycle, and the summed value is compared to a predetermined harvest count value that ensures adequately frozen ice. When the summed value exceeds the harvest count value, the controller operates the heater and rake to harvest the ice from the mold. The calculations are time and temperature dependent and therefore the controller, unlike known controllers employing fixed temperature and cam-driven controls, efficiently and accurately determines when ice is frozen and ready for harvesting based on temperature conditions of the mold and an integration of time and temperature conditions. Ice production is consequently optimized.
In another aspect of the invention, the controller is programmed to delay a harvest of ice, based upon the position of the feeler arm, for a pre-selected time after the summed value exceeds the harvest count value. Premature harvesting is therefore avoided when a storage bin or ice bucket is removed from the refrigerator or appliance.
In a further aspect of the invention, the controller is programmed to execute a harvest fix algorithm when ice is not harvested within a predetermined time period. Specifically, the controller operates the heater at an elevated temperature when in the harvest fix mode, and de-energizes the motor for a predetermined time period to clear obstructions in the icemaker and avoid associated service calls.
In yet another aspect of the invention, the controller is programmed to determine whether the mold is full of water based upon a reading from the thermistor. Specifically, the controller opens a water valve to fill the mold with water for a predetermined time period, reads a signal from the thermistor; and determines whether the mold is full based upon a change, or lack thereof, in the thermistor reading. If desired, additional filling periods may be executed for pre-selected times to fill the mold to a desired level. Thus, inefficient freezing of a less than full mold is avoided.
Implemented by solid state electronics and logic-driven controls, a more efficient, accurate, and reliable icemaker system is provided.